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Topology of cell adhesion molecules
J W Becker1, H P Erickson, S Hoffman
1Rockefeller University, New York, NY 10021.
Summary
Neural cell adhesion molecule (N-CAM) and liver cell adhesion molecule (L-CAM) share similar rod-shaped structures with flexible hinges. These structural features, not homophilic binding sites, are crucial for effective cell-cell adhesion.
Area of Science:
- Cell adhesion molecules
- Structural biology
- Biochemistry
Background:
- Neural cell adhesion molecule (N-CAM) exists in multiple forms (ld, sd, ssd) with varying cytoplasmic domains.
- Liver cell adhesion molecule (L-CAM) is a distinct single-species molecule.
- Both N-CAM and L-CAM possess large extracellular regions and can be released as fragments (Fr2 and Ft1, respectively).
Purpose of the Study:
- To elucidate the structural characteristics of different N-CAM forms and L-CAM fragments.
- To investigate the molecular basis of N-CAM aggregation and cell adhesion.
- To compare the structural similarities between N-CAM and L-CAM.
Main Methods:
- Electron microscopy of rotary shadowed molecules.
- Characterization of N-CAM and L-CAM fragments (Fr2, Ft1).
- Immunolabeling with specific antibodies targeting N-CAM domains and binding sites.
Main Results:
- All examined N-CAM forms and L-CAM fragments exhibit rod-shaped structures with flexible hinges.
- N-CAM ld/sd chains form rosettes through interactions involving transmembrane/cytoplasmic domains, not homophilic binding sites.
- Antibody labeling indicates specific binding sites on N-CAM, including the distal ends and near the hinge region.
Conclusions:
- The general rod-shaped configuration and flexible hinge of N-CAM and L-CAM are critical for cell-cell adhesion.
- N-CAM aggregation is mediated by interactions within their cytoplasmic domains.
- Structural similarities between N-CAM and L-CAM suggest conserved mechanisms for cell adhesion.